JP4384695B2 - Method for cooling rolled steel - Google Patents

Description

The present invention relates to a cooling method for cooling a long rolled steel material such as a hot-rolled rail.

Railway rails used in heavy-duty railways and curved sections are required to have higher wear resistance than ordinary rails. For this reason, after hot rolling, the process which raises the intensity | strength of a rail head by accelerated cooling is performed until a pearlite transformation is complete | finished from austenite range temperature. In recent years, in order to further improve wear resistance, a pearlite rail having an increased carbon content up to the hypereutectoid region has been developed and put into practical use (see Patent Document 1).

However, when the amount of carbon is increased in order to improve wear resistance, pro-eutectoid cementite tends to be generated on the rail head, and there is a problem that the toughness and ductility of the rail are greatly reduced.
Therefore, in Patent Document 2, in order to suppress the generation of proeutectoid cementite in the rail column and to stably generate a pearlite structure having a high cementite ratio and a high hardness in the rail head, the rail head is formed in the austenite region. A pearlite system that accelerates and cools at 1 to 10 ° C./s from 700 to 500 ° C., and further accelerates and cools the rail column at 1 to 10 ° C./s from austenite temperature to 750 to 600 ° C. A method for manufacturing a rail is disclosed.

On the other hand, as an accelerated cooling method for rails, (1) a method using mist (see Patent Documents 3 to 5) and (2) a method using a gas such as air (see Patent Documents 6 and 7) depending on the cooling medium. (3) A method of immersing the rail head in a coolant (see Patent Documents 8 and 9) is known.

JP-A-8-144016 JP-A-9-137228 JP 47-7606 A JP 54-147124 A JP-A-8-319515 JP-A 61-149436 JP-A 61-279626 JP-A-57-85929 JP-A-8-170120

In order to stably generate a pearlite structure in high carbon rail steel, it is necessary to increase the cooling rate during accelerated cooling. However, when this is attempted to be realized by the conventional accelerated cooling method described above, there are the following problems.

When the droplet comes into contact with the hot object, a vapor film is formed between the droplet and the hot object, and a Leidenfrost phenomenon occurs in which the droplet floats on the hot object. In the methods (1) and (3) using a liquid as the cooling medium, the vapor film formed on the rail surface obstructs the contact between the rail and the cooling medium, resulting in variations in the cooling rate. As a result, when the temperature deviation occurs in the rail and the temperature deviation increases, the steel structure may also vary.

Further, the method (2) using a gas as a cooling medium has a drawback that the cooling rate is slower than the liquid cooling method.

The present invention has been made in view of such circumstances, and a method for cooling a rolled steel material capable of significantly improving the cooling rate by suppressing the formation of a vapor film on the surface of a long rolled steel material and capable of uniform accelerated cooling. The purpose is to provide.

In order to achieve the above-mentioned object, the present invention is a cooling method for cooling a hot-rolled long rolled steel material, wherein a nozzle plate having a plurality of nozzle holes is arranged at the outlet and injects cooling water. a chamber having a cooling water supply nozzle in the interior, with the air outlet of the chamber disposed along the rolling steel so as to face the rolled steel, injecting the cooling water from the cooling water supply nozzle, before Symbol A rectifying plate is disposed between the gas inlet and the cooling water supply nozzle so that the cooling pressurized gas introduced from the gas inlet provided in the chamber does not directly hit the nozzle plate. to press the water from behind, it said from the gas inlet to supply cooling compressed gas, a cooling medium consisting of a mixture of the cooling water and the cooling compressed gas is sprayed from the nozzle plate It is characterized by performing the uniform cooling of the rolled steel.

When a liquid is used as the cooling medium, a large cooling capacity can be ensured, but the cooling rate varies due to the vapor film formed on the surface of the rolled steel material, resulting in uneven cooling. Therefore, in the present invention, a cooling water supply nozzle for injecting cooling water is installed in a chamber for injecting a cooling pressurized gas from the air outlet in which a nozzle plate having a plurality of nozzle holes is arranged toward the rolled steel material. , Mist injection of the cooling medium, which is a mixture of pressurized gas for cooling and cooling water, from the nozzle plate in the direction perpendicular to the surface of the rolled steel material increases the collision speed of the water droplets, and the water droplets adhering to the rolled steel material quickly. Remove. Thereby, formation of the vapor film is hindered, and uniform cooling is possible without changing the cooling rate.

In addition, although the use of the nozzle of the high air-water ratio which raised the ratio of the pressurized gas for cooling with respect to cooling water is also considered, if it is going to cool a long rolled steel material uniformly at once, many nozzles will be needed. In addition, since maintenance of nozzles frequently occurs, it is not realistic as industrial equipment.

When looking at the discharge distribution in the longitudinal direction of the chamber, that is, in the longitudinal direction of the rolled steel material, the discharge amount in the vicinity of the gas inlet is the largest, and the discharge amount increases as the distance from the gas inlet increases. Decrease. In this state, when cooling water is sprayed from the cooling water supply nozzle toward the nozzle plate, water droplets are pushed by the cooling pressurized gas from behind in the vicinity of the gas inlet where the flow of the cooling pressurized gas is strong. The amount of water sprayed from the nozzle plate is reduced. As a result, the amount of water varies in the entire chamber.
Therefore, in the present invention, a rectifying plate is installed between the gas introduction port and the cooling water supply nozzle so that the cooling pressurized gas introduced from the gas introduction port flows through the rectification plate to the entire chamber. This prevents variation in the amount of water in the entire chamber.

In the method for cooling a rolled steel material according to the present invention, it is preferable that a ratio of a volume flow rate of the cooling pressurized gas to a volume flow rate of the cooling water is 1000 to 50000.
The ratio of the volumetric flow rate of the cooling pressurized gas to the volumetric flow rate of the cooling water is called the air / water ratio.
In the case of a high air / water ratio, the vapor film formed on the surface of the rolled steel material is eliminated by the pressurized gas for cooling, so the formation of the vapor film is hindered and stable cooling is ensured. At this time, when the air / water ratio is less than 1000, the cooling rate varies greatly, and when the air / water ratio exceeds 50000, the cooling effect is saturated.

Moreover, in the cooling method of the rolled steel material which concerns on this invention, it is preferable to make the said cooling water supply nozzle orient | assign to the said nozzle plate, and to inject the said cooling water.

In the method for cooling a rolled steel material according to the present invention, it is preferable that the pressurized gas for cooling is air or nitrogen.
In the present invention, the kind of the cooling medium is not limited, but air or nitrogen is preferable from the viewpoint of ease of handling and economy.

In the method for cooling a rolled steel material according to the present invention, the cooling water may be jetted from the cooling water supply nozzle in a mist shape, a shower shape, or a flowing water shape.

It has been confirmed by experiments by the present inventors that the particle size distribution of the mist ejected from the nozzle plate has almost the same tendency regardless of the particle size of the water droplet ejected from the cooling water supply nozzle. The reason for this is that the cooling water sprayed in the chamber once merges in the nozzle plate, and the combined cooling water is redispersed when sprayed from the nozzle holes of the nozzle plate together with the cooling pressurized gas. It is thought that.
Accordingly, the cooling water to be injected may be in the form of mist, shower, or flowing water, and only the cooling water may be injected from the cooling water supply nozzle, or the cooling water and the pressurized pressurized gas may be mixed. You may spray. In short, a predetermined amount of water may be supplied onto the nozzle plate.

Moreover, in the cooling method of the rolled steel material which concerns on this invention, it is preferable that the collision speed at the time of the said cooling medium colliding with the surface of the said rolled steel material shall be 50-200 m / s.
It has been found that the higher the collision speed, the higher the cooling speed, and when the collision speed is 50 m / s or more, the variation in the cooling speed is reduced to about ± 1.5 ° C. If the collision speed exceeds 200 m / s, the cooling effect is saturated.

In the method for cooling a rolled steel material according to the present invention, the cooling start temperature of the rolled steel material after hot rolling is set to an austenite region temperature or higher, and the cooling end temperature of the rolled steel material is set to 450 to 600 ° C. preferable.
This is because quenching does not occur unless the cooling start temperature is not lower than the austenite temperature and the cooling end temperature is not higher than 600 ° C., which is not preferable. On the other hand, if accelerated cooling is continued to less than 450 ° C., a martensite structure is generated in the rail head portion, so that the hardness increases but the toughness decreases, which is not preferable.

Further, in the method for cooling a rolled steel material according to the present invention, when the rolled steel material is a rail, the nozzle is disposed above the rail with a gap and disposed facing the top of the rail. The cooling medium is ejected from the plate toward the top of the head, and the chamber is disposed at a side of the rail with a gap, and the nozzle plate disposed to face the head side of the rail. It is preferable to inject the cooling medium toward the head side portion. By doing in this way, mist injection can be performed in the direction perpendicular to the surface of the rail head.

In the method for cooling a rolled steel material according to the present invention, cooling water for injecting cooling water into a chamber for injecting a cooling pressurized gas toward the rolled steel material from a blowout port in which a nozzle plate having a plurality of nozzle holes is arranged. A supply nozzle is installed, and the cooling medium mixed with pressurized gas for cooling and cooling water is sprayed from the nozzle plate in the direction perpendicular to the surface of the rolled steel material to increase the collision speed of water droplets. Remove adhering water droplets quickly. As a result, formation of a vapor film is hindered, uniform cooling is possible without changing the cooling rate, and stable accelerated cooling is also possible.

In addition, a rectifying plate is installed between the gas inlet and the cooling water supply nozzle so that the cooling pressurized gas introduced from the gas inlet flows uniformly throughout the chamber through the rectifying plate. Thus, variation in the amount of water in the entire chamber can be prevented.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In the following description, a rail is taken as an example of a long rolled steel material.

The cooling devices 10 and 20 used in the method for cooling a rolled steel material according to an embodiment of the present invention are cooling devices that cool the hot-rolled rail 30, and as shown in FIG. The cooling device 10 is disposed so as to face the head top portion 31, and the cooling device 20 is disposed so as to face the both head side portions 32. The distance between the cooling device 10 and the top 31 of the rail 30 and the distance between the cooling device 20 and the head side 32 of the rail 30 are set to a level of several mm to several tens mm.
Each cooling device 10, 20 has a shape elongated in the rail 30 direction in plan view (the longitudinal dimension is about 1000 to 5000 mm), and extends over the entire length of the rail 30 along the longitudinal direction of the rail 30. It is arranged continuously.
Hereinafter, the individual cooling devices 10 and 20 will be described in detail.

The cooling device 10 has a gas inlet 13 for introducing air (an example of a pressurized pressurized gas) sent from a blower (not shown) in the upper part, and has a box-like shape in which a downstream end is a blower outlet 12. A cooling water supply nozzle 15 for injecting the cooling water supplied through the pipe 17 toward the top 31 of the rail 30 is installed in the chamber 11 so that the cooling water is pushed by the gas from behind. Yes.

The chamber 11 includes a widened portion 11a having a gas inlet 13 provided at an upper portion thereof, and a reduced width portion 11c connected to the widened portion 11a via a tapered inclined portion 11b, and downstream of the reduced width portion 11c. A nozzle plate 14 having a plurality of nozzle holes 14 c (see FIG. 2) is attached to the air outlet 12 provided at the end on the side so as to be parallel to the top 31 of the rail 30. Further, between the gas inlet 13 and the cooling water supply nozzle 15, air introduced from the gas inlet 13 does not directly hit the nozzle plate 14 at a portion corresponding to the gas inlet 13 in the chamber 11. In addition, a rectifying plate 16 is installed.

On the other hand, the cooling device 20 also has a gas introduction port 23 for introducing air sent from a blower (not shown), and a side end portion of the cooling device 20 is formed in a box-shaped chamber 21 having a blow-out port 22 through a pipe 27. The cooling water supply nozzle 25 for injecting the cooling water supplied in this way toward the head side portion 32 of the rail 30 is installed, and the cooling water is pushed from behind by the gas, similarly to the cooling device 10 for the top portion 31. It is composed.

The chamber 21 has a widened portion 21a in which a gas inlet 23 is provided on a side portion, and a narrowed portion 21c connected to the widened portion 21a via a tapered inclined portion 21b. A nozzle plate 24 having a plurality of nozzle holes is attached to the outlet 22 provided at the downstream end so as to be parallel to the head side portion 32 of the rail 30. Further, a rectifying plate 26 is installed between the gas inlet 23 and the cooling water supply nozzle 25 so that the gas flows in a balanced manner (balanced) throughout the chamber 21.

Next, the nozzle plate 14, the cooling water supply nozzle 15, and the rectifying plate 16 constituting the cooling device 10 will be described in detail. The nozzle plate 24, the cooling water supply nozzle 25, and the rectifying plate 26 of the cooling device 20 are also substantially similar. It is the same.

As shown in FIG. 2, the nozzle plate 14 is regularly formed with a large number of nozzle holes 14c having a diameter of about 2 to 10 mm, for example, with a predetermined interval (for example, an interval of about 2 to 10 mm). Further, the width W in the short direction (the width direction of the rail 30) of the region where the nozzle hole 14c is formed so that the mist is perpendicular to the entire width of the top portion 31 of the rail 30 is the width of the top portion 31 of the rail 30. It is almost the same.

As shown in FIG. 3, the cooling water supply nozzle 15 is attached to each end of a plurality of branch pipes 17 a branched downward from a pipe 17 arranged in the longitudinal direction of the chamber 11. The cooling water sprayed from the cooling water supply nozzle 15 may be in the form of mist, shower, or flowing water. Further, only the cooling water may be injected from the cooling water supply nozzle 15, or the cooling water and air may be mixed and injected.

Water droplets ejected from the cooling water supply nozzle 15 are ejected toward the nozzle plate 14, and the water density of the mist ejected from the nozzle plate 14 is uniform (see FIGS. 4A and 4B). .

As shown in FIG. 5, the rectifying plate 16 is disposed directly below at least a portion corresponding to the gas inlet 13 of the chamber 11 in plan view. As a result, the air introduced from the gas inlet 13 is distributed uniformly throughout the chamber 11 via the rectifying plate 16, and the amount of water due to the position of the chamber 11 is prevented.

Although not shown, a large number of holes are formed in the current plate, and the total area per unit area of the holes formed immediately below each of the plurality of gas inlets is the unit area of the holes formed in other locations. The mist ejected from the nozzle plate 14 may be uniform in the longitudinal direction of the chamber 11 by making it smaller than the total area of the hits.

FIG. 6A is a graph showing the air discharge distribution and the mist water density ratio in a state in which there is no rectifying plate in the chamber 11 (see FIG. 6B). The distance between the cooling water supply nozzle 15 and the nozzle plate 14 is 100 mm, the interval between the adjacent cooling water supply nozzles 15 is 500 mm, and the gas inlet 13 is located at the center between the cooling water supply nozzles 15 (distance and All intervals are test examples).
When there is no rectifying plate in the chamber 11, the amount of air discharged in the longitudinal direction of the chamber 11 is large directly under the gas inlet 13 and decreases as the distance from the gas inlet 13 increases. When mist is injected from the cooling water supply nozzle 15 in this state, the mist is pushed by the air just below the gas inlet 13 where the air flow is strong, and the amount of mist injected from the nozzle plate 14 decreases. For this reason, the amount of water in the longitudinal direction of the chamber 11 is not uniform.

FIG. 7A shows the air discharge distribution and the mist water density in a state where the rectifying plate 16 having an appropriate shape is installed immediately below the gas inlet 13 under the conditions of FIG. 6 (see FIG. 7B). It is the graph which showed the ratio. The distance between the current plate 16 and the nozzle plate 14 is 185 mm (test example).
When the rectifying plate 16 is installed directly under the gas inlet 13, the air introduced into the chamber 11 from the gas inlet 13 once collides with the rectifying plate 16 and then is dispersed throughout the chamber 11. The amount of air ejected from 14 is uniform throughout the chamber 11.

Since the air introduced from the gas inlet 13 also flows in the longitudinal direction of the chamber 11 through the rectifying plate 16, the water amount distribution in the longitudinal direction of the chamber 11 becomes uniform.

When the rail head is cooled using the cooling devices 10 and 20 having the above-described configuration, the air / water ratio of the cooling medium composed of a mixture of air and cooling water sprayed from the nozzle plates 14 and 24 is 1000 to 50000, The cooling medium is mist-injected toward the top 31 from the nozzle plate 14 disposed facing the top 31 of the rail 30 at a collision speed of mist to the rail head of 50 to 200 m / s. The cooling medium is mist-injected from the nozzle plate 24 disposed opposite to the head side portion 32 toward the head side portion 32 to uniformly cool the rail head portion between the austenite region temperature and 450 to 600 ° C. .

FIG. 8 is a graph showing the relationship between the collision speed of the mist and the cooling speed obtained by the experiment.
The cooling water supply nozzle was a nozzle BIM J 2015 manufactured by Ikeuchi Co., Ltd., and the test specimen was a 141-lb rail with a length of 100 mm, and a thermocouple embedded at a depth of 2 mm from the top of the specimen was used. .
The specimen was heated to 820 ° C. in a heating furnace, then taken out and cooled by the present cooling device from 750 ° C., and cooled to 500 ° C. or lower. Cooling conditions were set such that the discharge cooling water density was constant at 70 L (liter) / m ² · min, and the amount of air was changed to set the mist collision speed to 5, 20, 50, 150, and 200 m / s. . The air pressure at this time was 1.1 to 1.2 atm.

The mist collision speed Va was calculated by the following equation, where the discharge speed was Ve, the distance between the outlet and the rail was h, and the outlet diameter was d.
Va = 6.39 × Ve / (h / d + 0.6)

The experiment was conducted 10 times for each impact speed, and the cooling speed was determined from the time required for the indicated value of the thermocouple from 750 ° C. to 500 ° C. As a result, it was found that the higher the collision speed, the higher the cooling speed, and when the collision speed was 50 m / s or more, the variation in the cooling speed was reduced to about ± 1.5 ° C. and stabilized. In addition, when the collision speed exceeds 200 m / s, it is not realistic because the facility is enlarged and the running cost is increased.

Table 1 shows the relationship between the air / water ratio and the cooling rate. From the table, it is understood that when the air / water ratio is 1000 or more, the standard deviation of the cooling rate is 2.2 or less, the effect is saturated at the air / water ratio of 50000, and stable cooling is possible. FIG. 9 is a graph of the data in Table 1.

In addition, when cooling the pillar part and foot part of a rail using this cooling device, since the cooling rate of these parts becomes faster than a head, it is necessary to set cooling conditions separately.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the above-described embodiments, and is considered within the scope of the matters described in the claims. Other embodiments and modifications are also included. For example, in the above embodiment, the pressurized gas for cooling introduced into the chamber is air, but it may be nitrogen.

It is a schematic diagram which shows the cooling device used for the cooling method of the rolled steel materials which concern on one embodiment of this invention. It is a top view of the nozzle plate of the cooling device. It is a perspective view of piping and a cooling water supply nozzle part which supply cooling water. (A) is the schematic diagram which showed the injection condition of the cooling water supply nozzle, (B) is the graph which showed the result. It is a perspective view of a baffle plate. (A) is the graph which showed the discharge distribution of the air in the state without a baffle plate in a chamber, and the water quantity density ratio of mist, (B) is the schematic diagram which showed the flow of the air in the chamber in the same state It is. (A) is the graph which showed the discharge distribution of the air in the state where the baffle plate was installed directly under the blower, and the water volume density ratio of the mist, and (B) shows the flow of air in the chamber in the same state. It is a schematic diagram. It is the graph which showed the relationship between the collision speed of a mist and a cooling rate. It is the graph which showed the relationship between the air-water ratio and the variation in cooling rate.

Explanation of symbols

10: Cooling device, 11: Chamber, 11a: Widened part, 11b: Inclined part, 11c: Reduced part, 12: Blowing outlet, 13: Gas inlet, 14: Nozzle plate, 14c: Nozzle hole, 15: Cooling water Supply nozzle, 16: current plate, 17: piping, 17a: branch pipe, 20: cooling device, 21: chamber, 21a: widened portion, 21b: inclined portion, 21c: narrowed portion, 22: air outlet, 23: gas Inlet, 24: Nozzle plate, 25: Cooling water supply nozzle, 26: Rectifying plate, 27: Piping, 30: Rail (rolled steel), 31: Top part, 32: Head side part

Claims (7)

A cooling method for cooling a hot rolled long steel sheet,
A nozzle plate having a plurality of nozzle holes is arranged at the outlet, and a chamber having a cooling water supply nozzle for injecting cooling water therein is provided along the rolled steel so that the outlet of the chamber faces the rolled steel. Te arranged, while injecting the cooling water from the cooling water supply nozzle,
As before Symbol chamber is introduced from the gas inlet port provided in the cooling gas under pressure is not directly exposed to the nozzle plate, by placing the rectifying plate between the cooling water supply nozzle and the gas inlet, the cooling water so as to push from behind, said from the gas inlet to supply cooling compressed gas, by injecting a cooling medium consisting of a mixture of the cooling water and the cooling compressed gas from said nozzle plate And the cooling method of the rolled steel materials characterized by performing the uniform cooling of the said rolled steel materials. In the cooling method for rolled steel according to claim 1 Symbol mounting method of cooling rolled steel characterized by a 1,000 to 50,000 the ratio of the volume flow rate of the cooling compressed gas to the volume flow rate of the cooling water. 3. The method for cooling a rolled steel material according to claim 1, wherein the pressurized gas for cooling is air or nitrogen. 4. The method for cooling a rolled steel material according to any one of claims 1 to 3 , wherein the cooling water is injected from the cooling water supply nozzle into a mist shape, a shower shape, or a flowing water shape. Cooling method. The rolling steel material cooling method according to any one of claims 1 to 4 , wherein a collision speed when the cooling medium collides with a surface of the rolled steel material is 50 to 200 m / s. Steel cooling method. In the cooling method of the rolled steel materials of any one of Claims 1-5 , while making the cooling start temperature of the said rolled steel materials after hot rolling more than an austenite area temperature, the cooling end temperature of this rolled steel materials is 450. A method for cooling a rolled steel material, characterized in that the temperature is ˜600 ° C. The method for cooling a rolled steel material according to any one of claims 1 to 6 , wherein the rolled steel material is a rail, the chamber is disposed above and to the side of the rail with a gap, and the rail A method for cooling a rolled steel material, characterized in that the cooling medium is sprayed from the nozzle plate disposed to face the top and the side of the head toward the top and the side of the head.

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